diff --git a/singletons-default.cabal b/singletons-default.cabal
--- a/singletons-default.cabal
+++ b/singletons-default.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           singletons-default
-version:        0.1.0.6
+version:        0.1.0.7
 synopsis:       An optional type with type level default
 description:    dependently typed optional values with default
 category:       Data
diff --git a/src/Data/Default/Singletons.hs b/src/Data/Default/Singletons.hs
--- a/src/Data/Default/Singletons.hs
+++ b/src/Data/Default/Singletons.hs
@@ -389,7 +389,6 @@
 Construct a rational type in reduced form.
 -}
 type family (%) z n :: Q where
-  Pos 0 % 0 = Pos 0 :% 0
   Pos p % q = Pos (Div p (GCD p q)) :% Div q (GCD p q)
   NegOneMinus p % q
     = Neg (Div (1 + p) (GCD (1 + p) q))
@@ -399,6 +398,7 @@
 Construct the greatest common divisor of `Natural` types.
 -}
 type family GCD (a :: Natural) (b :: Natural) :: Natural where
+  GCD 0 0 = 1
   GCD 0 b = b
   GCD a 0 = a
   GCD a b = GCD b (Mod a b)